11th Bio Botany · Part

Learning Objectives Chapter Outline . Attributes of Living organisms . Viruses . Classification of Living world . Bacteria . Fungi Earth was formed some . billion years ago. It is the life supporting planet with land forms like mountains, plateaus, glaciers, etc. Life on earth exists within a complex structure called biosphere . There exist many mysteries and wonders in the living world some are not Living World Reproduction Reproduction is one of the fundamental characteristic features of living organisms. It is the tendency of a living organism to perpetuate its own species. There are two types of reproduction namely asexual and sexual (Figure . ). Nucleus (a) (b) (c) (d) Figure . : Types of Asexual Reproduction (a) Conidia formation- Penicillium , (b) Budding-Yeast, (c) Fragmentation- Spirogyra, (d) Regeneration- Planaria Asexual reproduction refers to the production of the progeny possessing features more or less similar to those of parents. The sexual reproduction brings out variation through recombination. Asexual reproduction in living organisms occurs by the production of conidia ( Aspergillus, Penicillium ), budding ( Hydra and Yeast), binary fission (Bacteria and Amoeba ) fragmentation ( Spirogyra ), protonema (Mosses) and regeneration ( Planaria ). Exceptions are the sterile worker bees and mules. Response to stimuli All organisms are capable of sensing their environment and respond to various physical, chemical and biological stimuli. Animals sense . Attributes of living organisms The attributes of living organisms are given below and is represented in Figure . . Excretion Irritability Respiration Metabolism ATTRIBUTES OF LIVING ORGANISMS Movement Nutrition Growth Reproduction Figure . : Attributes of living organisms Growth Growth is an intrinsic property of all living organisms through which they can increase cells both in number and mass. Unicellular and multicellular organisms grow by cell division. In plants, growth is indefinite and occurs throughout their life. In animals, growth is definite and occurs for some period. Growth in non-living objects is extrinsic . Mountains, boulders and sand mounds grow by simple aggregation of material on the surface. Living cells grow by the addition of new protoplasm within the cells. Therefore, growth in living thing is intrinsic . In unicellular organisms like Bacteria and Amoeba growth occurs by cell division and such cell division also leads to the growth of their population. Hence, growth and reproduction are mutually inclusive events. Cellular structure All living organisms are made up of cells which may be prokaryotic or eukaryotic. Prokaryotes are unicellular, lack membrane bound nuclei and organelles like mitochondria, endoplasmic reticulum, golgi bodies and so on (Example: Bacteria and Blue green algae). In Eukaryotes a definite nucleus and membrane bound organelles are present. Eukaryotes may be unicellular ( Amoeba ) or multicellular ( Oedogonium ). Atoms Mixture Molecules & Compounds Crystals Organelles Colloids Living cells Tissues Organs Organ systems Individual organism Population Community Ecosystem Biosphere Non Living Living Ecosystem Individual organism Living cells I II III Figure . : The levels of organization and integration in living organism Activity . Collect Vallisneria leaves or Chara from nearby aquarium and observe a leaf or Chara thallus (internodal region)under the microscope. You could see cells clearly under the microscope. Could you notice the movement of cytoplasm? The movement of cytoplasm is called cytoplasmic streaming or cyclosis . . Viruses Did you go through the headlines of newspapers in recent times? Have you heard of the terms EBOLA, ZIKA, AIDS, SARS, H1N1 etc.? There are serious entities which are considered as “Biological Puzzle” and cause disease in man. They are called viruses. We have learnt about the attributes of living world in the previous chapter. Now we shall discuss about viruses which connect the living and nonliving world. their surroundings by sense organs. This is called Consciousness . Plants also respond to the stimuli. Bending of plants towards sunlight, the closure of leaves in touch-me-not plant to touch are some examples for response to stimuli in plants. This type of response is called Irritability. Homeostasis Property of self-regulation and tendency to maintain a steady state within an external environment which is liable to change is called Homeostasis . It is essential for the living organism to maintain internal condition to survive in the environment. Metabolism The sum of all the chemical reactions taking place in a cell of living organism is called metabolism . It is broadly divided into anabolism and catabolism. The difference between anabolism and catabolism is given in Table . . Table . : Difference between anabolism and catabolism Anabolism Catabolism Building up process Breaking down process Smaller molecules combine together to form larger molecule Larger molecule break into smaller units Chemical energy is formed and stored The stored chemical energy is released and used Example: Synthesis of proteins from amino acids Example: Breaking down of glucose to CO and water Movement, Nutrition, Respiration and Excretion are also considered as the property of living things. The levels of organization in living organism begin with atoms and end in Biosphere . Each level cannot exist in isolation instead they form levels of integration as given in Figure . . i. Cuboid symmetry – Example: Adenovirus, Herpes virus. ii. Helical symmetry – Example: Influenza virus, TMV. iii. Complex or Atypical – Example: Bacteriophage, Vaccinia virus. (a) Adenovirus, (b) Tobacco Mosaic virus, (c) T Bacteriophage Figure . : Shapes of Viruses Protein DNA Fibre Capsid RNA Head DNA Collar Sheath Basal plate Tail fibre (a) ( b) (c) . . Characteristic Features of Viruses Living Characters • Presence of nucleic acid and protein. • Capable of mutation • Ability to multiply within living cells. • Able to infect and cause diseases in living beings. • Show irritability. • Host –specific Non-living Characters • Can be crystallized. • Absence of metabolism. • Inactive outside the host. • Do not show functional autonomy. • Energy producing enzyme system is absent. . . Classification of Viruses Among various classifications proposed for viruses the classification given by David Baltimore in the year is given below. The classification is based on mechanism of RNA production, the nature of the genome (single stranded –ss or double stranded - ds), RNA or DNA, the use of reverse transcriptase (RT), ss RNA may be ( + ) sense or ( – ) antisense. Viruses are classified into seven classes (Table . ). Viral genome Each virus possesses only one type of nucleic acid either DNA or RNA. The nucleic acid may be in a linear or circular form. Generally The word virus is derived from Latin meaning ‘Poison’. Viruses are sub- microscopic, obligate intracellular parasites. They have nucleic acid core surrounded by protein coat. Viruses in their native state contain only a single type of nucleic acid which may be either DNA or RNA. The study of viruses is called Virology . An American Scientist obtained virus in crystallised form from infected tobacco juice in the year . He was jointly awarded “Nobel Prize” with Dr. J.H. Northrop for Chemistry in . W.M. Stanley ( - ) . . Milestones in Virology Edward Jenner used vaccination for small pox Adolf Mayer demonstrated the infectious nature of Tobacco mosaic virus using sap of mosaic leaves Dimitry Ivanowsky proved that viruses are smaller than bacteria M.W. Beijierink defined the infectious agent in tobacco leaves as ῾ Contagium vivum fluidum ’ F.W.Twort identified Viral infection in Bacteria d’Herelle coined the term ‘Bacteriophage’ Luc Montagnier and Robert Gallo discovered HIV (Human Immuno Deficiency Virus). . . Size and Shape Viruses are ultramicroscopic particles. They are smaller than bacteria and their diameter range from to nm. (1nm = - metres). Bacteriophage measures about - nm in size. The size of TMV is × nm. Generally viruses are of three types based on shape and symmetry (Figure . ). helical virus measuring about 300x20nm with a molecular weight of 39x10 Daltons. The virion is made up of two constituents, a protein coat called capsid and a core called nucleic acid . The protein coat is made up of approximately identical protein subunits called capsomeres which are present around a central single stranded RNA molecule. The genetic information necessary for the formation of a complete TMV particle is contained in its RNA. The RNA consists of , nucleotides. . . Bacteriophage Viruses infecting bacteria are called Bacteriophages . It literally means ‘eaters of bacteria’ (Gr: Phagein = to eat). Phages are abundant in soil, sewage water, fruits, vegetables, and milk. Structure of T bacteriophage The T phage is tadpole shaped and consists of head, collar, tail, base plate and fibres (Figure . ). The head is hexagonal which consists of about identical protein subunits. The long helical tail consists of an inner tubular core which is connected to the head by a collar. There is a base plate attached to the end of tail. The base plate contains six spikes and tail fibres. These fibres are used to attach the phage on the cell wall of bacterial host during replication. A dsDNA molecule of about µm is tightly packed inside the head. The DNA is about times longer than the phage itself. . . Multiplication or Life Cycle of Phages Phages multiply through two different types of life cycle. a. Lytic or Virulent cycle b. Lysogenic or Avirulent life cycle. a. Lytic Cycle During lytic cycle of phage, disintegration of host bacterial cell occurs and the progeny virions are released (Figure .5a). The steps involved in the lytic cycle are as follows: nucleic acid is present as a single unit but in wound tumour virus and in influenza virus it is found in segments. The viruses possessing DNA are called ‘Deoxyviruses’ whereas those possessing RNA are called ‘Riboviruses’ . Majority of animal and bacterial viruses are DNA viruses (HIV is the animal virus which possess RNA). Plant viruses generally contain RNA (Cauliflower Mosaic virus possess DNA). The nucleic acids may be single stranded or double stranded. On the basis of nature of nucleic acid viruses are classified into four Categories. They are Viruses with ssDNA (Parvo viruses), dsDNA (Bacteriophages), ssRNA (TMV)and dsRNA(Wound Tumour Virus). Table . : Different Classes of viruses Class Example Class – Viruses with dsDNA Class –Viruses with ( + ) sense ssDNA Class – Viruses with dsRNA Class – Viruses with ( + )sense ssRNA Class – Viruses with ( – )sense ssRNA Class – Viruses with ( + ) sense ssRNA –RT: that replicate with DNA intermediate in life cycle Class – Viruses with ds DNA –RT: that replicate with RNA intermediate in life cycle Adeno viruses Parvo viruses Reo viruses Toga viruses Rhabdo viruses Retro viruses Hepadna viruses . . Tobacco Mosaic Virus (TMV) Tobacco mosaic virus was discovered in by Dimitry Ivanowsky from the Tobacco plant. Viruses infect healthy plants through vectors like aphids, locusts etc. The first visible symptom of TMV is discoloration of leaf colour along the veins and show typical yellow and green mottling which is the mosaic symptom. The downward curling and distortion of young apical leaves occurs, plant becomes stunted and yield is affected. Structure Electron microscopic studies have revealed that TMV is a rod shaped (Figure .4b) (v) Release The phage particle gets accumulated inside the host cell and are released by the lysis of host cell wall. Figure . : Multiplication cycle of phage Bacterial genome Capsid DNA Phage DNA Host cell Release of new phage particle Adsorption Penetration Synthesis Assembly and maturation Release Phage Phage DNA Bacterial chromosome Circular phage DNA Prophage Reproducing bacterial cell (a) Lytic cycle (b) Lysogenic cycle b. Lysogenic Cycle In the lysogenic cycle the phage DNA gets integrated into host DNA and gets multiplied along with nucleic acid of the host. No independent viral particle is formed (Figure .5b). As soon as the phage injects its linear DNA into the host cell, it becomes circular and integrates into the bacterial chromosome by recombination. The integrated phage DNA is now called prophage. The activity of the prophage gene is repressed by two repressor proteins which are synthesized by phage genes. This checks the synthesis of new phages within the host cell. However, each time the bacterial (i) Adsorption Phage (T ) particles interact with cell wall of host ( E. coli ). The phage tail makes contact between the two, and tail fibres recognize the specific receptor sites present on bacterial cell surface. The lipopolysaccharides of tail fibres act as receptor in phages. The process involving the recognition of phage to bacterium is called landing . Once the contact is established between tail fibres and bacterial cell, tail fibres bend to anchor the pins and base plate to the cell surface. This step is called pinning. (ii) Penetration The penetration process involves mechani- cal and enzymatic digestion of the cell wall of the host. At the recognition site phage digests certain cell wall structure by viral enzyme (lysozyme). After pinning the tail sheath contracts (using ATP) and appears shorter and thicker. After contraction of the base plate enlarges through which DNA is injected into the cell wall without using met- abolic energy. The step involving ­injection of DNA particle alone into the bacterial cell is called Transfection . The empty protein coat leaving outside the cell is known as ‘ghost’ . (iii) Synthesis This step involves the degradation of bacterial chromosome, protein synthesis and DNA replication. The phage nucleic acid takes over the host biosynthetic machinery. Host DNA gets inactivated and breaks down. Phage DNA suppresses the synthesis of bacterial protein and directs the metabolism of the cell to synthesis the proteins of the phage particles and simultaneously replication of Phage DNA also takes place. (iv) Assembly and Maturation The DNA of the phage and protein coat are synthesized separately and are assembled to form phage particles. The process of assembling the phage particles is known as maturation . After minutes of infection, about new phages are assembled. Viruses infecting blue green algae are called Cyanophages and are first reported by Safferman and Morris in the year (Example LPP1 - Lyngbya, Plectonema and Phormidium ). Similarly, Hollings( ) reported viruses infecting cultivated Mushrooms and causing die back disease. The viruses attacking fungi are called Mycoviruses or Mycophages. . . Viral diseases Viruses are known to cause disease in plants, animals and Human beings (Figure . ). A list of viral disease is given in Table . . (a) Figure . : Viral diseases ( a) Mosaic disease of tomato, (b) Symptom of Chicken pox (b) Blister like ­pustules cell divides, the prophage multiplies along with the bacterial chromosome. On exposure to UV radiation and chemicals the excision of phage DNA may occur and results in lytic cycle. Virion is an intact infective virus particle which is non-replicating outside a host cell. Viroid is a circular molecule of ssRNA without a capsid and was discovered by T.O.Diener in the year . The RNA of viroid has low molecular weight. Viroids cause citrus exocortis and potato spindle tuber disease in plants. Virusoids were discovered by J.W.Randles and Co-workers in .They are the small circular RNAs which are similar to viroids but they are always linked with larger molecules of the viral RNA. Prions were discovered by Stanley B. Prusiner in the year and are protein- aceous infectious particles. They are the caus- ative agents for about a dozen ­fatal ­degenerative disorders of the ­central ­nervous system of humans and other ­animals. For example Creutzfeldt – Jakob Disease (CJD), Bovine Spongiform Encephalopathy (BSE) – com- monly known as mad cow disease and scrapie disease of sheep. Table . : Viral diseases Plant diseases Animal diseases Human diseases .Tobacco mosaic . Cauliflower mosaic . Sugarcane mosaic . Potato leaf roll . Bunchy top of banana . Leaf curl of papaya . Vein clearing of Lady’s finger . Rice Tungro disease . Cucumber mosaic . Tomato mosaic disease . Foot and mouth disease of cattle . Rabies of dog . Encephalomyelitis of horse . Common cold . Hepatitis B . Cancer . SARS(Severe Acute Respiratory Syndrome) . AIDS(Acquired Immuno Deficiency Syndrome) . Rabies . Mumps . Polio . Chikungunya . Small Pox . Chicken pox . Measles Streaks on Tulip flowers are due to Tulip Breaking Virus which belong to Potyviridae group. Viruses of Baculoviridae group are commercially exploited as insecticides. Cytoplasmic Polyhedrosis Granulo viruses and Entomopox viruses were employed as potential insecticides. . Classification of Living World From the previous chapter we know that the planet earth is endowed with living and non -living things. In our daily life we see several things in and around us. Imagine, you are on a trip to Hill station. You are enjoying the beauty of mountains, dazzling colour of the flowers, and melodious sound of the birds. You may be capturing most of the things you come across in the form of photography. Now, from this experience can you mention the objects you have come across? Can you record your observations and tabulate them?. How will you organize the things? Will you place mountain and flowers together or tall trees and trailing herbs in one category or place it in different category? If you place it in different category, what made you to place them in different category? So classification is essential and could be done only by understanding and comparing the things based on some characters. In this chapter we shall learn about classification of living world. Many attempts have made in the past to classify the organisms on earth. Theophrastus , “Father of Botany” used the morphological characters to classify plants into trees, shrubs and herbs. Aristotle classified animals into two groups. i.e., Enaima (with red blood) and Anaima (without red blood). Carl Linnaeus classified living world into two groups namely Plants and Animals based on morphological characters. His classification faced major setback because Prokaryotes and Eukaryotes were grouped together. Similarly fungi, heterotrophic organisms were placed along with the photosynthetic plants. In course of time, the development of tools compelled taxonomists to look for different areas like cytology, anatomy, embryology, molecular biology, phylogeny etc., for classifying organisms on earth. Thus, new dimensions to classifications were put forth from time to time. . . Need of Classification Classification is essential to achieve following needs. • To relate things based on common characteristic features. • To define organisms based on the salient features. • Helps in knowing the relationship amongst different groups of organisms. • It helps in understanding the evolutionary relationship between organisms. . . Classification of Living World A comparison of classification proposed for classification of living world is given in Table . . . . Five Kingdom Classification R.H.Whittaker, an American taxonomist proposed five Kingdom classification in the year . The Kingdoms include Monera, Table . : Systems of Classification Two Kingdom Three Kingdom Four Kingdom Five Kingdom Carl Linnaeus ( ) Ernst Haeckel ( ) Copeland ( ) R.H. Whittaker ( ) . Plantae . Animalia . Protista . Plantae . Animalia . Monera . Protista . Plantae . Animalia . Monera . Protista . Fungi . Plantae . Animalia Table . : Comparison of Five Kingdoms Criteria Kingdom Monera Protista Fungi Plantae Animalia Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic Level of organization Mostly Unicellular, rarely multicellur Unicellular Multicellular and unicellular Tissue/organ Tissue/organ/organ system Cell wall Present (made up of Peptidoglycan and Mucopeptides) Present in some (made up of cellulose), absent in others Present (made up of chitin or cellulose) Present (made up of cellulose) absent Nutrition Autotrophic (Phototrophic, Chemoautotrophic) Heterotrophic (parasitic and saprophytic) Autotrophic- Photosynthetic. Heterotrophic Heterotrophic- parasitic or Saprophytic Autotrophic (Photosynthetic) Heterotrophic (Holozoic) Motility Motile or non-motile Motile or non-motile Non-motile Mostly Non-motile Mostly motile Organisms Archaebacteria, Eubacteria, Cyanobacteria, Actinomycetes and Mycoplasma Chrysophytes, Dinoflagellates, Euglenoids, Slime molds, Amoeba, Plasmodium, Trypanosoma, Paramecium Yeast, Mushrooms and Molds Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms Sponges, Invertebrates and Vertebrates Protista, Fungi, Plantae and Animalia (Figure . ). The criteria adopted for the classification include cell structure, thallus organization, mode of nutrition, reproduction and phylogenetic relationship . A comparative account of the salient features of each Kingdom is given in Table . Merits • The classification is based on the complexity of cell structure and organization of thallus. • It is based on the mode of nutrition • Separation of fungi from plants • It shows the phylogeny of the organisms Demerits • The Kingdom Monera and protista accommodate both autotrophic and heterotrophic organisms, cell wall lacking and cell wall bearing organisms thus making these two groups more heterogeneous. • Viruses were not included in the system. Carl Woese and co-workers in the year introduced three domains of life viz., Bacteria , Archaea and Eukarya based on the difference in rRNA nucleotide sequence, lipid structure of the cell membrane. A revised six Kingdom classification for living world was proposed by Thomas Cavalier-Smith in the year and the Kingdom Monera is divided in to Archaebacteria and Eubacteria. Recently Ruggierio et al ., published a seven Kingdom classification which is a practical extension of Thomas Cavalier’s six Kingdom scheme. According to this classification there are two Super Kingdoms. ( Prokaryota and Eukaryota ) Prokaryota includes two Kingdoms namely Archaebacteria and Eubacteria. Eukaryota includes the Protozoa, Chromista, Fungi, Plantae and Animalia. A new Kingdom, the Chromista was erected and it included all algae whose chloroplasts contain chlorophyll a and c, as well as various colourless forms that are closely related to them. Diatoms, Brown algae, Cryptomonads and Oomycetes were placed under this Kingdom. Activity . Visit to a pond and record the names of the biotic components of it with the help of your teacher. Tabulate the data and segregate them according to Five Kingdom Classification. Red tide is caused by toxic bloom of Dinoflagellates like Gymnodinium breve and Gonyaulax tamarensis . A major red tide incident in west coast of Florida in the year killed Hundreds and thousands of fishes. . Bacteria Bacteria Friends or Foes? Have you noticed the preparation of curd in our home? A little drop of curd turns the milk into curd after some time. What is responsible for this change? Why it Sours? The change is brought by Lactobacillus lactis , a bacterium present in the curd. The sourness is due to the formation of Lactic Anne ne nelida Ne Ne Nematoda Spe pe permatophyta a Charophytaa Bry ryo yophyta Rhodophyt hyta hyta Chlorophyta h Phaeophhyta Pteridophyta Ascom om myco a Basidiomycota e Vertebrate ordata o Protocho a Echinodermata Chaetognatha Coelenterata era fera Porifer phora Cilioph pho hizopoda Rhizopod Rhizopod ria r Bacter Mollusca Mastigophora ra ran Protista Monera Oomycete Bacillariophyta Zygomycota mycete myce Myxomyce Platyhelminthes Dictyostelii Dictyos Dictyosteliidae Animalia Fungi Plantae Arthropoda Cyanophyta ota a d Figure . : Five Kingdom Classification but some are autotrophic and possess Bacteriochlorophyll ( Chromatium ) • They reproduce vegetatively by Binary fission and endospore formation. • They exhibit variations which are due to genetic recombination and is achieved through conjugation, transformation and transduction. The shape and flagellation of the bacteria varies and is given in Figure . . Figure . : Shape and flagellation in bacteria Monotrichous Lophotrichous Amphitrichous Peritrichous Atrichous Diplobacillus Bacillus Spirillum Vibrio Coccus Staphylococcus Tetracoccus Sarcina Streptococcus Diplococcus . . Ultrastructure of a Bacterial cell The bacterial cell reveals three layers (i) Capsule/Glycocalyx (ii) Cell wall and (iii) Cytoplasm (Figure . ). Capsule/Glycocalyx Some bacteria are surrounded by a gelatinous substance which is composed of polysaccharides or polypeptide or both. A thick layer of glycocalyx bound tightly to the acid. Have you been a victim of Typhoid? It is a bacterial disease caused by Salmonella typhi, a bacterium. So we can consider this prokaryotic organism as friend and foe, due to their beneficial and harmful activities. Robert Koch ( – ) Robert Heinrich Hermann Koch was a German physician and microbiologist. He is considered as the founder of modern bacteriology. He identified the causal organism for Anthrax, Cholera and Tuberculosis. The experimental evidence for the concept of infection was proved by him (Koch’s postulates). He was awarded Nobel prize in Medicine/Physiology in the year . . . Milestones in Bacteriology C.G. Ehrenberg coined the term Bacterium Christian Gram introduced Gram staining method David H. Bergy published First edition of Bergey’s Manual Fredrick Griffith discovered Bacterial transformation Joshua Lederberg discovered of Plasmid Bacteria are prokaryotic, unicellular, ubiq- uitous, microscopic organisms. The study of Bacteria is called Bacteriology. Bacteria were first discovered by a Dutch scientist, Anton van Leeuwenhoek in and were called “animalcules”. . . General characteristic features of Bacteria • They are Prokaryotic organisms and lack nuclear membrane and membrane bound organelles. • The Genetic material is called nucleoid or genophore or incipient nucleus • The cell wall is made up of Polysaccharides and proteins • Most of them lack chlorophyll, hence they are heterotrophic ( Vibrio cholerae ) Plasma membrane Mesosom Cell wall Nucleoid (DNA) Cytoplasm Flagellum Plasmid Inclusion Polyribosome Pilus Capsule Figure . : Ultrastructure of a bacterial cell cell wall is called capsule . It protects cell from desiccation and antibiotics. The sticky nature helps them to attach to substrates like plant root surfaces, Human teeth and tissues. It helps to retain the nutrients in bacterial cell. Duodenal and Gastric ulcers are caused by Helicobacter pylori, a Gram negative bacterium • Bt toxin from Bacillus thuringiensis finds application in raising insect resistant crops (Bt Crops). Cell wall The bacterial cell wall is granular and is rigid. It provides protection and gives shape to the cell. The chemical composition of cell wall is rather complex and is made up of peptidoglycan or mucopeptide (N-acetyl glucosamine, N-acetyl muramic acid and peptide chain of or aminoacids). One of the most abundant polypeptide called porin is present and it helps in the diffusion of solutes. Plasma membrane The plasma membrane is made up of lipoprotein. It controls the entry and exit of small molecules and ions. The enzymes involved in the oxidation of metabolites (i.e., the respiratory chain) as well as the photosystems used in photosynthesis are present in the plasma membrane. Cytoplasm Cytoplasm is thick and semitransparent. It contains ribosomes and other cell inclusions. Cytoplasmic inclusions like glycogen, poly-β- hydroxybutyrate granules, sulphur granules and gas vesicles are present. Bacterial chromosome The bacterial chromosome is a single circular DNA molecule, tightly coiled and is not enclosed in a membrane as in Eukaryotes. This genetic material is called Nucleoid or Genophore. It is amazing to note that the DNA of E.coli which measures about 1mm long when uncoiled, contains all the genetic information of the organism. The DNA is not bound to histone proteins. The single chromosome or the DNA molecule is circular and at one point it is attached to the plasma membrane and it is believed that this attachment may help in the separation of two chromosomes after DNA replication. Plasmid Plasmids are extra chromosomal double stranded, circular, self-replicating, autonomous elements. The size of a plasmid varies from to kb usually plasmids contribute to about . to . % of the total DNA of bacteria. They contain genes for ­fertility, antibiotic resistant and heavy metals. It also help in the production of bacteriocins and toxins which are not found in bacterial chromosome. The number of plasmids per cell varies. Plasmids are classified into different types based on the function. Some of them are F (Fertility) factor, R ­(Resistance) plasmids, Col (Colicin) plasmids, Ri (Root ­inducing) plasmids and Ti (Tumour inducing) plasmids. Mesosomes These are localized infoldings of plasma membrane produced into the cell in the form of vesicles, tubules and lamellae. They are clumped and folded together to maximize their surface area and helps in respiration and in binary fission. Polysomes / Polyribosomes The ribosomes are the site of protein synthesis. The number of ribosome per cell varies from , to , . The ribosomes are 70S type and consists of two subunits (50S and 30S). The ribosomes are held together by mRNA and form polyribosomes or polysomes. Flagella Certain motile bacteria have numerous thin hair like projections of variable length emerge from the cell wall called flagella. It is – μm in diameter and μm in length. The flagella of Eukaryotic cells contain + microtubles but each flagellum in bacteria is made up of a single fibril. Flagella are used for locomotion. Based on the number and position of flagella there are different types of bacteria (Figure . ) Fimbriae or Pili Pili or fimbriae are hair like appendages found on surface of cell wall of gram-negative bacteria (Example: Enterobacterium ). The pili are . to µm long with a diameter of about .025µm. In addition to normal pili there are special type of pili which help in conjugation called sex pili are also found. . . Gram staining procedure The Gram staining method to differentiate bacteria was developed by Danish Physician Christian Gram in the year1884. It is a differential staining procedure and it classifies bacteria into two classes - Gram positive and Gram negative. The steps involved in Gram staining procedure is given in Figure . . The Gram positive bacteria retain crystal violet and appear dark violet whereas Gram negative type loose the crystal violet and when counterstained by safranin appear red under a microscope. Most of the gram positive cell wall contain considerable amount of teichoic acid and teichuronic acid. In addition, they may contain polysaccharide molecules. The gram negative cell wall contains three components that lie outside the peptidoglycan layer. . Lipoprotein . Outer membrane .Lipopolysaccharide. Thus the different results in the gram stain Table . : Difference between Gram Positive and Gram Negative Bacteria S. No. Characteristics Gram positive Bacteria Gram negative Bacteria . Cell wall Thick layered with ( . µm- .02µm) Thin layered with ( .0075µm– .012µm) . Rigidity of cell wall Rigid due to presence of Peptidoglycans Elastic due to presence of lipoprotein- polysaccharide mixture . Chemical composition Peptidoglycans- % Polysaccharide- % Teichoic acid present Peptidoglycans- to % rest is polysaccharides and lipoproteins. Teichoic acid absent . Outer membrane Absent Present . Periplasmic space Absent Present . Susceptibility to penicillin Highly susceptible Low susceptible . Nutritional requirements Relatively complex Relatively simple . Flagella Contain basal body rings Contain basal body rings . Lipid and lipoproteins Low High . Lipopolysaccharides Absent Present Figure . : Steps involved in Gram Staining Prepare a smear of bacterial culture Stain with Crystal violet for seconds Rinse in distilled water for seconds Grams Iodine for minute Rinse in distilled water Wash in % ethanol or acetone for to seconds Rinse in distilled water Safranin for – seconds Rinse in distilled water and blot Observe under microscope Nutrition On the basis of their mode of nutrition bacteria are classified into two types namely autotrophs and heterotrophs. I Autotrophic Bacteria Bacteria which can synthesise their own food are called autotrophic bacteria. They may be further subdivided as A. Photoautotrophic bacteria Bacteria use sunlight as their source of energy to synthesize food. They may be . Photolithotrophs In photolithotrophs the hydrogen donor is an inorganic substance. a. Green sulphur bacteria: In this type of bacteria the hydrogen donor is H S and possess pigment called Bacterioviridin. Example: Chlorobium. b. Purple sulphur bacteria: For bacteria belong to this group the hydrogen donor is thiosulphate, Bacteriochlorophyll is present . Chlorophyll containing chlorosomes are present Example: Chromatium . . Photoorganotrophs They utilize organic acid or alcohol as hydrogen donor. Example: Purple non sulphur bacteria – Rhodospirillum. B. Chemoautotrophic bacteria They do not have photosynthetic pigment hence they cannot use sunlight energy. This type of bacteria obtain energy from organic or inorganic substance. . Chemolithotrophs This type of bacteria oxidize inorganic compound to release energy. Examples: . Sulphur bacteria - Thiobacillus thiooxidans . Iron bacteria - Ferrobacillus ferrooxidans . Hydrogen bacteria - Hydrogenomonas . Nitrifying bacteria - Nitrosomonas and Nitrobacter are due to differences in the structure and composition of the cell wall. The difference between Gram Positive and Gram negative bacteria is given in Table . . What are Magnetosomes ? Intracellular chains of - magnetite (Fe O ) particles are found in bacterium Aquaspirillum magnetotacticum . and it help the bacterium to locate nutrient rich sediments. . . Life processes in Bacteria Respiration Two types of respiration are found in Bacteria. They are . Aerobic respiration . Anaerobic respiration. . Aerobic respiration These bacteria require oxygen as terminal acceptor and will not grow under anaerobic conditions. (i.e. in the absence of O ) Example: Streptococcus. Obligate aerobes Some Micrococcus species are obligate aerobes (i.e. they must have oxygen to survive). . Anaerobic respiration These bacteria do not use oxygen for growth and metabolism but obtain their energy from fermentation reactions. Example: Clostridium. Facultative anaerobes There are bacteria that can grow ­either using oxygen as a terminal electron ­acceptor or anaerobically using fermentation reaction to obtain energy. When a facultative anaerobe such as E. coli is present at a site of infection like an abdominal ­abscess, it can rapidly consume all ­available O and change to anaerobic metabolism producing an anaerobic environment and thus allow the anaerobic bacteria that are present to grow and cause disease. Example: Escherichia coli and ­Salmonella. Capnophilic Bacteria Bacteria which require CO for their growth are called as capnophilic bacteria. Example: Campylobacter. and Clostridium tetani. Endospores are thick walled resting spores. During favourable condition, they germinate and form bacteria. Sexual Reproduction Typical sexual reproduction involving the formation and fusion of gametes is absent in bacteria. However gene recombination can occur in bacteria by three different methods they are . Conjugation . Transformation . Transduction . Conjugation J. Lederberg and Edward L. Tatum demonstrated conjugation in E. coli . in the year . In this method of gene transfer the donor cell gets attached to the recipient cell with the help of pili. The pilus grows in size and forms the conjugation tube. The plasmid of donor cell which has the F + (fertility factor) undergoes replication. Only one strand of DNA is transferred to the recipient cell through conjugation tube. The recipient completes the structure of double stranded DNA by synthesizing the strand that complements the strand acquired from the donor (Figure . ). F plasmid Conjugation pilus Chromosome F + cell F + cell F + cell F - cell Figure . : Conjugation . Transformation Transfer of DNA from one bacterium to another is called transformation (Figure . ). In the bacteriologist Frederick Griffith . Chemoorganotrophs This type of bacteria oxidize organic compounds to release energy. Examples: . Methane bacteria – Methanococcus . Acetic acid bacteria – Acetobacter . Lactic acid bacteria – Lactobacillus II. Heterotrophic Bacteria They are Parasites ( Mycobacterium ) Saprophytes ( Bacillus mycoides ) or Symbiotic (Rhizobium in root nodules of leguminous crops). . . Reproduction in Bacteria Bacteria reproduces asexually by binary fission, conidia and endospore formation (Figure . ). Among these, binary fission is the most common one. Binary fission Under favourable conditions the cell divides into two daughter cells. The nuclear material divides first and it is followed by the formation of a simple median constriction which finally results in the separation of two cells. ( a) ( b) Daughter cells Cell wall Nucleoid Endospore Thick wall Figure . : Asexual Reproduction in Bacteria (a) Binary fission, (b) Endospore Endospores During unfavourable condition bacteria produce endospores. Endospores are produced in Bacillus megaterium , Bacillus sphaericus DNA of another strain into the former is called Transformation. . Transduction Zinder and Lederberg ( ) discovered Transduction in Salmonella typhimurum . Phage mediated DNA transfer is called Transduction (Figure . ). Transduction is of two types (i) Generalized transduction (ii) Special- ized or Restricted transduction (i) Generalized Transduction The ability of a bacteriophage to carry genetic material of any region of bacterial DNA is called generalised transduction. (ii) Specialized or Restricted Transduction The ability of the bacteriophage to carry only a specific region of the bacterial DNA is called specialized or restricted transduction. demonstrated transformation in Mice using Diplococcus pneumoniae . Two strains of this bacterium are present. One strain produces smooth colonies and are virulent in nature (S-type). In addition another strain produce rough colonies and are avirulent (R-type). When S-type of cells were injected into the mouse, the mouse died. When R-type of cells were injected, the mouse survived. He injected heat killed S-type cells into the mouse. The mouse did not die. When the mixture of heat killed S-type cells and R-type cells were injected into the mouse, the mouse died. The avirulent rough strain of Diplococcus had been transformed into S-type cells. The hereditary material of heat killed S-type cells had transformed R-type cell into virulent smooth strains. Thus the phenomenon of changing the character of one strain by transferring the Figure . : Transduction in Bacteria Phage Phage DNA phage particle particle Recipient Cell Bacterial chromosome Virulent Defective Defective Generalised Transduction Specialised Transduction Figure . : Transformation in Bacteria (a) Griffith’s experiment on Transformation (b) Mechanism of Transformation Mouse lives M li Mouse dies M di Mouse lives M li Mouse dies M di R-Strain Heat-Killed S-Strain killed S- Strain S-Strain R-Strain and Heat- (a) (b) Donar cell Donar DNA Host DNA Recipient cell Integration . . Economic importance of Bacteria Bacteria are both beneficial and harmful. The beneficial activities of bacteria are given in table . . Table . : Economic importance of Bacteria Beneficial aspects Bacteria Role . Soil fertility Ammonification . Bacillus ramosus . Bacillus mycoides Convert complex proteins in the dead bodies of plants and animals into ammonia which is l